Low-loss operation of silicon-on-insulator integrated components at 2.6-2.7†µm.

Development of mid-infrared photonics is gaining attention, driven by a multitude of sensing applications requiring increasingly compact and cost-effective photonics systems. To this end, low-loss operation of µm-scale silicon-on-insulator photonic integration elements is demonstrated for the 2.6-2.7 µm wavelength region. The platform utilizes the 3 µm thick silicon core layer technology enabling demonstration of low-loss and low birefringence waveguides. Measurements of record low single mode waveguide propagation losses of 0.56 ± 0.09 dB/cm and bend losses <0.08 dB for various miniaturized bend geometries are presented and validated by simulation. Furthermore, a wavelength filter based on echelle grating that allows to select several operating channels within the 2.64-2.7 µm band, with a linewidth of ∼1.56 nm for each channel is presented.

Compact multi-million Q resonators and 100 MHz passband filter bank in a thick-SOI photonics platform.

We demonstrate ring and racetrack resonators with Qs of 3.8 to 7.5 million and 100 MHz bandwidth racetrack resonator filters, implemented in a thick silicon-on-insulator foundry platform that features a 3 µm thick device layer. We show that special racetrack resonators (with weakly guiding straight sections that transition to strongly confining bends) implemented in this platform can be preferable to rings for applications such as integrated microwave-photonic signal processing that require filters with sub-GHz bandwidth, tens of GHz of free spectral range (FSR), and a compact footprint for dense system-on-chip integration. We demonstrate ring resonators with 7.5×106 intrinsic Q, but limited FSR of 5.1 GHz and a taxing footprint of 21mm2 due to a large 2.6 mm bend-loss-limited radius. In comparison, we demonstrate two racetrack resonator designs with intrinsic Qs of 3.8×106 and 4.3×106, larger respective FSRs of 11.6 GHz and 7.9 GHz, and less than 1/20th the area of the ring resonator. Using racetrack resonators, we implemented a four-channel, 100 MHz wide passband filter bank with 4.2 to 5.4 dB insertion loss to drop ports.

Precise length definition of active GaAs-based optoelectronic devices for low-loss silicon photonics integration.

The length variation associated with standard cleaving of III-V optoelectronic chips is a major source of loss in the integration with the micron-scale silicon-on-insulator waveguides. To this end, a new, to the best of our knowledge, approach for precise definition of the III-V chip length is reported. The method employs lithography and wet etching of cleave marks outside the active III-V waveguides. The marks follow a specific crystallographic orientation and are used to initiate and guide the cleaving process. Besides minimizing the air gap between the butt-coupled III-V and Si waveguides and hence minimizing the coupling losses, the use of precisely defined length significantly improves the integration yield owing to the increased length uniformity. We apply this technique to defining the lengths of GaAs-based semiconductor optical amplifiers and demonstrate length control with an accuracy better than 250 nm per facet. This variation is more than 1 order of magnitude smaller than with the traditional cleaving methods, resulting in improvement of coupling by several dBs.

Multiplexed mycotoxins determination employing white light reflectance spectroscopy and silicon chips with silicon oxide areas of different thickness.

Biosensing through White Light Reflectance Spectroscopy (WLRS) is based on monitoring the shift of interference spectrum due to the binding reactions occurring on top of a thin SiO2 layer deposited on a silicon chip. Multi-analyte determinations were possible through scanning of a single sensor chip on which multiple bioreactive areas have been created. Nonetheless, the implementation of moving parts increased the instrumentation size and complexity and limited the potential for on-site determinations. Thus, in this work, a new approach, which is based on patterning the sensor surface to create areas with different SiO2 thickness, is developed and evaluated for multi-analyte determinations with the WLRS set-up. The areas of different thickness can be interrogated by a single reflection probe placed on a fixed position over the chip and the reflection spectrum recorded is de-convoluted to the spectra corresponding to each area allowing the simultaneous monitoring of the bioreactions taking place at each one of them. The combination of different areas thickness was optimized using chips with two areas for single analyte assays. The optimum chips were then used for the simultaneous determination of two mycotoxins, aflatoxin B1 and fumonisin B1. A competitive immunoassay format was followed employing immobilization of mycotoxin-protein conjugates onto the SiO2 of different thickness. It was found that the dual-analyte assays had identical analytical characteristics with the respective single-analyte ones. The detection limits achieved were 0.05 ng/mL for aflatoxin B1 and 1.0 ng/mL for fumonisin B1, with dynamic ranges extending up to 5.0 and 50 ng/mL, respectively. The sensor was also evaluated for the determination of the two mycotoxins in whole grain samples (wheat and maize). The extraction protocol was optimized and recoveries ranging from 85 to 115% have been determined. Due to lack of moving parts, the novel multi-analyte format is expected to considerably facilitate the built-up of a portable device for determination of analytes at the point-of-need.

Roll-to-roll fabrication of integrated PDMS-paper microfluidics for nucleic acid amplification.

Microfluidic-based integrated molecular diagnostic systems, which are automated, sensitive, specific, user-friendly, robust, rapid, easy-to-use, and portable, can revolutionize future medicine. Current research and development largely relies on polydimethylsiloxane (PDMS) to fabricate microfluidic devices. Since the transition from the proof-of-principle phase to clinical studies requires a vast number of integrated microfluidic devices, there is a need for a high-volume manufacturing method of silicone-based microfluidics. Here we present the first roll-to-roll (R2R) thermal imprinting method to fabricate integrated PDMS-paper microfluidics for molecular diagnostics, which allows production of tens of thousands of replicates in an hour. In order to validate the replicated molecular diagnostic platforms, on-chip amplification of viral ribonucleic acid (RNA) with loop-mediated isothermal amplification (LAMP) was demonstrated. These low-cost, rapid and accurate molecular diagnostic platforms will generate a wide range of applications in preventive personalized medicine, global healthcare, agriculture, food, environment, water monitoring, and global biosecurity.

Data transmission at 1300 nm using optical interposer comprising hybrid integrated silicon waveguide and dilute nitride electroabsorption modulator.

High speed back-to-back transmission of NRZ data at 12.5 Gbit/s was achieved over a repeaterless optical network without the use of forward error correction or optical clock recovery using a hybrid integrated silicon photonics optical interconnect. The interconnect comprises an electroabsorption modulator based on dilute nitride multiple quantum well material on GaAs substrate optically coupled to large core silicon waveguide using passive alignment and flip-chip bonding.

MMI resonators based on metal mirrors and MMI mirrors: an experimental comparison.

We report, to the best of our knowledge, the first experimental proof of MMI-based resonators. The resonators have been designed and fabricated on a micron-scale silicon photonics platform and are based on different reflectors suitably placed on two of the four ports of 2x2 MMIs with uneven splitting ratios, namely 85:15 and 72:28. The reflectors are either based on aluminum mirrors or on all-dielectric MMI mirrors. Performances of the different designs are compared with each other and with numerical simulations. Finesse values as high as 13.1 (9.9) have been measured in best aluminum (all-dielectric) resonators, corresponding to a quality factor of 5.8·10(3) (12.5·10(3)) and mirror reflectivity exceeding 92% (88%).

Unconstrained splitting ratios in compact double-MMI couplers.

A novel guided-wave optical power coupler is presented, based on two 2x2 50/50 multimode interference splitters connected with tapered waveguides that play the role of a phase shifter. By simply changing the length of this phase shifter, these double-MMI couplers can be easily designed to get any desired splitting ratio. Results of simulations are discussed and compared with the characterizations of devices fabricated on micron-scale SOI wafers, to highlight pros and cons of the proposed solution. The fabricated splitters have been found to have average losses about 0.4 ± 0.5 dB and splitting ratios ranging from 56/44 to 96/4.

Dramatic size reduction of waveguide bends on a micron-scale silicon photonic platform.

We demonstrate theoretically and experimentally how highly multimodal high index contrast waveguides with micron-scale cores can be bent, on an ultra-broad band of operation, with bending radii below 10 µm and losses for the fundamental mode below 0.02 dB/90°. The bends have been designed based on the Euler spiral and fabricated on 4 µm thick SOI. The proposed approach enabled also the realization of 180° bends with 1.27 µm effective radii and 0.09 dB loss, which are the smallest low-loss bends ever reported for an optical waveguide. These results pave the way for unprecedented integration density in most semiconductor platforms.