Heterogeneous integration of Si photodiodes on silicon nitride for near-visible light detection.

Silicon nitride (SiN) is used extensively to complement the standard silicon photonics portfolio. However, thus far demonstrated light sources and detectors on SiN have predominantly focused on telecommunication wavelengths. Yet, to unlock the full potential of SiN, integrated photodetectors for wavelengths below 850 nm are essential to serve applications such as biosensing, imaging, and quantum photonics. Here, we report the first, to the best of our knowledge, microtransfer printed Si p-i-n photodiodes on a commercially available SiN platform to target wavelengths <850 nm. A novel heterogeneous integration process flow was developed to offer a high microtransfer printing yield. Moreover, these devices are fabricated with CMOS compatible and wafer-scale technology.

Transfer-print integration of GaAs p-i-n photodiodes onto silicon nitride waveguides for near-infrared applications.

We demonstrate waveguide-detector coupling through the integration of GaAs p-i-n photodiodes (PDs) on top of silicon nitride grating couplers (GCs) by means of transfer-printing. Both single device and arrayed printing is demonstrated. The photodiodes exhibit dark currents below 20 pA and waveguide-referred responsivities of up to 0.30 A/W at 2V reverse bias, corresponding to an external quantum efficiency of 47% at 860 nm. We have integrated the detectors on top of a 10-channel on-chip arrayed waveguide grating (AWG) spectrometer, made in the commercially available imec BioPIX-300 nm platform.

High-power single transverse and polarization mode VCSEL for silicon photonics integration.

We demonstrate a 6.5 mW single transverse and polarization mode GaAs-based oxide-confined VCSEL at 850 nm. High power is enabled by a relatively large oxide aperture and an epitaxial design for low resistance, low optical loss, and high slope efficiency VCSELs. With the oxide aperture supporting multiple polarization unrestrained transverse modes, single transverse and polarization mode operation is achieved by a transverse and polarization mode filter etched into the surface of the VCSEL. While the VCSEL is specifically designed for light source integration on a silicon photonic integrated circuit, its performance in terms of power, spectral purity, polarization, and beam properties are of great interest for a large range of applications.

Microfluidic-controlled optical router for lab on a chip.

In multiplexed analysis, lab on a chip (LoC) devices are advantageous due to the low sample and reagent volumes required. Although optical detection is preferred for providing high sensitivity in a contactless configuration, multiplexed optical LoCs are limited by the technological complexity for integrating multiple light sources and detectors in a single device. To address this issue, we present a microfluidic-controlled optical router that enables measurement in four individual optical channels using a single light source and detector, and without movable parts. The optofluidic device is entirely fabricated in polydimethylsiloxane (PDMS) by soft-lithography, compatible with standard microfabrication technologies, enabling monolithic integration in LoCs. In the device, in-coupled light from an optical fiber is collimated by a polymeric micro-lens and guided through a set of four sequentially connected micro-chambers. When a micro-chamber is filled with water, light is transmitted to the next one. If it is empty of liquid, however, total internal reflection (TIR) occurs at the PDMS-air interface, re-directing the light to the output optical fiber. The router presents high performance, with low cross-talk (<2%) and high switching frequencies (up to 0.343 ± 0.006 Hz), and provides a stable signal for up to 91% of the switching time. With this miniaturized, low-cost, simple and robust design, we expect the current technology to be integrated in the new generation of multiplexed photonic LoCs for biomarker analysis, even at the point of care.

Integration of high-speed GaAs metal-semiconductor-metal photodetectors by means of transfer printing for 850 nm wavelength photonic interposers.

We propose and demonstrate the integration of 850 nm GaAs-based metal-semiconductor-metal (MSM) photodetectors (PDs) based on transfer printing for application in photonic interposers. Both devices that directly interface with a multimode optical fiber (with device dimensions of 70 µm × 70 µm) as well as devices that interface with a SiN waveguide layer through a grating coupler (with device dimensions of 30 µm × 30 µm) are demonstrated. The dark currents are measured to be 22 nA and 7.2 nA at 2 V bias for the larger and smaller PDs respectively. For 850 nm wavelength, the external responsivities are measured to be 0.117 A/W and 0.1 A/W at 2 V bias. 20 GHz bandwidth is measured. Open 40 Gb/s eye diagrams are realized.