James Ferrara

Heterogeneously integrated long-wavelength VCSEL using silicon high contrast grating on an SOI substrate

We report an electrically pumped hybrid cavity AlGaInAs-silicon long-wavelength VCSEL using a high contrast grating (HCG) reflector on a silicon-on-insulator (SOI) substrate. The VCSEL operates at silicon transparent wavelengths ~1.57 μm with >1 mW CW power outcoupled from the semiconductor DBR, and single-mode operation up to 65 °C. The thermal resistance of our device is measured to be 1.46 K/mW. We demonstrate >2.5 GHz 3-dB direct modulation bandwidth, and show error-free transmission over 2.5 km single mode fiber under 5 Gb/s direct modulation. We show a theoretical design of SOI-HCG serving both as a VCSEL reflector as well as waveguide coupler for an in-plane SOI waveguide, facilitating integration of VCSEL with in-plane silicon photonic circuits. The novel HCG-VCSEL design, which employs scalable flip-chip eutectic bonding, may enable low cost light sources for integrated optical links.

Low loss hollow-core waveguide on a silicon substrate

Abstract Optical-fiber-based, hollow-core waveguides (HCWs) have opened up many new applications in laser surgery, gas sensors, and non-linear optics. Chip-scale HCWs are desirable because they are compact, light-weight and can be integrated with other devices into systems-on-a-chip. However, their progress has been hindered by the lack of a low loss waveguide architecture. Here, a completely new waveguiding concept is demonstrated using two planar, parallel, silicon-on-insulator wafers with high-contrast subwavelength gratings to reflect light in-between. We report a record low optical loss of 0.37 dB/cm for a 9-μm waveguide, mode-matched to a single mode fiber. Two-dimensional light confinement is experimentally realized without sidewalls in the HCWs, which is promising for ultrafast sensing response with nearly instantaneous flow of gases or fluids. This unique waveguide geometry establishes an entirely new scheme for low-cost chip-scale sensor arrays and lab-on-a-chip applications.

Heterogeneously Integrated Long-Wavelength VCSEL using High-Contrast Grating on Silicon

We report an electrically pumped AlGaInAs-silicon VCSEL using a high-contrast grating reflector on silicon. CW output power >1.5 mW, thermal resistance of 1.46 K/mW, and 5 Gb/s direct modulation is demonstrated.

Three-Dimensional Chirped High-Contrast Grating Hollow-Core Waveguide

A 3-D chirped high-contrast grating hollow-core waveguide (HCG-HW) exhibits highly efficient 2-D (transverse and lateral) light confinement. Compared with step-index ones, laterally chirped HCG-HWs (graded index) can pronouncedly reduce the propagation loss (>; 10×) without compromising the lateral index contrast. Simulation results show that a propagation loss as low as 0.04 dB/cm can be achieved. For a chirped HCG-HW with a 6-μm core height, it exhibits 30and 141-nm spectral widths for 0.1and 1-dB/cm loss requirements. The chirped HCG-HW also shows an ultralow nonlinear coefficient, which is on the order of 10-5 /W/m.

Chromatic dispersion variation and its effect on high-speed data signals due to structural parameter changes in a high-contrast-grating waveguide

High-contrast gratings hollow-core waveguides exhibit a low chromatic dispersion (8.6 ps/(nm·km)). High-speed (>;100 Gb/s), long-distance (30 m) and low-penalty (<;0.2 dB) on-chip data transmission can be achieved.

Tunable coloration with flexible high-contrast metastructures

We demonstrate novel high contrast metastructures with nearly all optical power concentrated in the -1st order diffraction and, when embedded in a flexible substrate, color change is achieved simultaneously in a multiple-color pattern by design.

Heterogeneously-integrated VCSEL using high-contrast grating on silicon

We present a unique heterogeneous integration approach for VCSELs on silicon using eutectic bonding. An electrically pumped III-V – silicon heterogeneous VCSEL is demonstrated using a high-contrast grating (HCG) reflector on silicon. CW output power >1.5 mW, thermal resistance of 1.46 K/mW, and 5 Gb/s direct modulation is demonstrated. We also explore the possibility of an all-HCG VCSEL structure that would benefit from stronger thermal performance, larger tuning efficiency, and higher direct modulation speeds.

Active coloration with flexible high contrast metastructures

The ability to actively control the perceived color of objects is highly desirable for a variety of applications, such as camouflage, sensing, and displays. Such a phenomenon can be readily found in nature - the chameleon is an excellent example. However, the capability to change color at-will has yet to be reproduced by humans. Ultra-thin dielectric high contrast metastructures (HCMs) have been shown to exhibit unique versatility to manipulate light. In this work, we report a completely new flexible HCM structure whose color can be varied by stretching the membrane. This is accomplished with a novel HCM design that annihilates the 0th order diffraction in a grating while enhancing the -1st order. The color perception of the HCM, determined by the -1st diffraction order, is thus easily changed with the variation of its period. The ultra-thin HCM is patterned on a silicon-on-insulator wafer and transferred onto a flexible membrane. We measure more than 15 times stronger intensity in the -1st order diffraction than the 0th order, in excellent agreement with theoretical results. We experimentally demonstrate brilliant colors and change the color of a 1 cm×1 cm sample from green to orange (39 nm wavelength change) with a stretch of 4.9% (25 nm period change). The same effect can be used for steering a laser beam. We demonstrate more than 40 resolvable beam spots.

Low-loss hollow-core waveguide using high-contrast sub-wavelength grating

We present a novel form of hollow-core waveguiding that enables chip-scale integration. Light propagates in air along a zig-zag path between very highly-reflective Si metastructures comprised of a single layer of sub-wavelength high-contrast gratings (HCGs) without the aid of sidewalls. Top and bottom subwavelength HCGs separated by 9um of air and with periodicity perpendicular to the propagation of light reflect light at shallow angles with extremely low loss. The HCGs are patterned on SOI wafers with 340 nm-thick Si device layers engraved in a single etch step, and have been measured to have a 0.37 dB/cm propagation loss. Our work demonstrates the light-guiding properties of HCG hollow-core waveguides with a novel form of lateral beam confinement that uses subtle reflection phase changes between core and cladding HCG regions capable of bending light around 30 mm radius-of-curvature tracks.