Broadband silicon nitride integrated polarization rotators at 780 nm.

Polarization management, and in particular polarization rotation, is becoming increasingly important for photonic integrated circuits (PICs). While fiber-optic networks are generally polarization insensitive, the large aspect ratio of high-index-contrast PIC waveguides leads to a large polarization-dependent response of integrated components such as waveguides, optical cavities, couplers, etc. Although foundry-processed polarization rotators operating at telecom and datacom wavelengths (C- and O-band) have been demonstrated, to date, there have been few reports of devices operating at shorter wavelengths. This work demonstrates silicon nitride (SiN) polarization rotators operating from λ=700-1000 nm (the I/Z-band) that take advantage of optical coupling between two waveguiding layers in a standard foundry process. We demonstrate a broadband white-light polarization measurement setup that enables precise characterization of the polarization-dependent transmission of photonic waveguide devices. Measurements on foundry-processed devices confirm full TE-to-TM rotation exhibiting a maximum polarization extinction ratio (PER) approaching 20 dB (limited by our measurement setup), and an exceptionally large bandwidth of up to 160 nm with an insertion loss less than 0.2 dB. Beam propagation method (3D-BPM) simulations show good agreement with experimental data and enable the device parameters to be adjusted to accommodate different operating wavelengths and geometries with no changes to the existing foundry process. This work opens up opportunities for applications in quantum information and bio-sensing where operation at λ<1000nm is needed.

Manufacture reliability assessment of Si photonic foundry fabricated slow-light photonic crystal waveguides.

Single-line-defect (W1) photonic crystal waveguides hold significant promise for various applications in integrated photonics due to their ability to induce slow light across wide photonic band ranges. Ensuring the manufacturing reliability of these devices is paramount for their practical implementation, as they tend to be highly sensitive to fabrication deviations. In this study, we investigated the manufacturing reliability of photonic crystal waveguides fabricated at the Albany Nanotech Complex foundry by comparing the consistency of band-edge locations and group indices across 14 chips. We also provide FIB images of the fabricated photonic crystals allowing an analysis of the sidewall quality of the holes.

High positional freedom SOI subwavelength grating coupler (SWG) for 300 mm foundry fabrication.

We present an apodized, single etch-step, subwavelength grating (SWG) high positional freedom (HPF) grating coupler based on the 220 nm silicon-on-insulator (SOI) with 2µm BOX substrate. The grating coupler was designed for 1550 nm light with transverse electric (TE) polarization. It has a measured maximum coupling efficiency of -7.49 dB (17.8%) and a -1 dB/-3 dB bandwidth of ~14 nm/29.5 nm respectively. It was fabricated in a 300mm state of the art CMOS foundry. This work presents an SOI-based grating coupler with the highest-to the best of our knowledge- -1 dB single mode fiber lateral alignment of 21.4 µm × 10.1 µm.

Mode-evolution-based coupler for high saturation power Ge-on-Si photodetectors.

We propose a mode-evolution-based coupler for high saturation power germanium-on-silicon photodetectors. This coupler uniformly illuminates the intrinsic germanium region of the detector, decreasing saturation effects, such as carrier screening, observed at high input powers. We demonstrate 70% more photocurrent generation (9.1-15.5 mA) and more than 40 times higher opto-electrical bandwidth (0.7-31 GHz) than conventional butt-coupled detectors under high-power illumination. The high-power and high-speed performance of the device, combined with the compactness of the coupling method, will enable new applications for integrated silicon photonics systems.

Immobilization mechanisms of deoxyribonucleic acid (DNA) to hafnium dioxide (HfO2) surfaces for biosensing applications.

Immobilization of biomolecular probes to the sensing substrate is a critical step for biosensor fabrication. In this work we investigated the phosphate-dependent, oriented immobilization of DNA to hafnium dioxide surfaces for biosensing applications. Phosphate-dependent immobilization was confirmed on a wide range of hafnium oxide surfaces; however, a second interaction mode was observed on monoclinic hafnium dioxide. On the basis of previous materials studies on these films, DNA immobilization studies, and density functional theory (DFT) modeling, we propose that this secondary interaction is between the exposed nucleobases of single stranded DNA and the surface. The lattice spacing of monoclinic hafnium dioxide matches the base-to-base pitch of DNA. Monoclinic hafnium dioxide is advantageous for nanoelectronic applications, yet because of this secondary DNA immobilization mechanism, it could impede DNA hybridization or cause nonspecific surface intereactions. Nonetheless, DNA immobilization on polycrystalline and amorphous hafnium dioxide is predominately mediated by the terminal phosphate in an oriented manner which is desirable for biosensing applications.

Direct attachment of DNA to semiconducting surfaces for biosensor applications.

In this work we propose a novel method of immobilizing nucleic acids for field effect or high electron mobility transistor-based biosensors. The naturally occurring 5' terminal phosphate group on nucleic acids was used to coordinate with semiconductor and metal oxide surfaces. We demonstrate that DNA can be directly immobilized onto ZrO(2), AlGaN, GaN, and HfO(2) while retaining its ability to hybridize to target sequences with high specificity. By directly immobilizing the probe molecule to the sensor surface, as opposed to conventional crosslinking strategies, the number of steps in device fabrication is reduced. Furthermore, hybridization to target strands occurs closer to the sensor surface, which has the potential to increase device sensitivity by reducing the impact of the Debye screening length.