Silicon photonics biosensors continue to be an area of active research, showing the potential to revolutionize Labon-
Chip applications ranging from environmental monitoring to medical diagnostics. As near-infrared light
propagates through nano-scale silicon wires on an SOI chip, a portion of the light resides outside the waveguide
and interacts with biomolecules and the biological matrix on the waveguide’s surface. This capability makes silicon
photonics an ideal platform for label-free biosensing. Additionally, the SOI platform is compatible with standard
CMOS fabrication processes, facilitating manufacturing at the economies of scale offered by today’s foundries. In
this paper, we describe our efforts to improve the performance of SOI-based biosensors—specifically, TE and TM
mode microring resonators, thin waveguide resonators, sub-wavelength grating resonators, as well as strip and slot
Bragg gratings. We compare device performance in terms of sensitivity, intrinsic limit of detection, and their
potential for biosensing applications in Lab-on-Chip systems.
Silicon photonics is going trough a terrific expansion driven by several applications, from chip wiring to integrated sensors and telecommunications. Some applications, e.g. intra and inter chip connections and sensing, require long parallel waveguides for wiring or for connecting grating couplers (GCs) to devices situated in sensing micro-channels. In well packed photonics chips there are often long wiring waveguides parallel for several mm, so loss can be caused by light coupled back and forth between them (cross-talk), by scattering, wall roughness, mode mismatch, etc. This work aims to investigate cross-talk for long parallel waveguides, and to propose methods to reduce cross-talk loss when high integration density is required.
We have designed and fabricated about 200 testing structures exploiting e-beam on silicon on insulator (SOI) chip, in order to test several parameters and to find out dominant loss mechanisms. All devices have been tested and measured using an automatic optical bench, in the wavelength range between 1500-1600 nm.
Achieved results are promising, since they allow for comparing cross-talk for short as well as long interaction lengths (up to 5 mm), different waveguide width pairs, several separation distances, and for TE and TM polarization. For smaller gaps, having not symmetric pair of waveguides is very beneficial, since it results in a lower power coupling, e.g. about 20/14 dB of crosstalk reduction for TE/TM waveguides after 5 mm of propagation and gap of 0.5 μm. This can be very useful for the design of integrated photonics chips requiring high-density packaging of devices and waveguides.
Silicon photonics is poised to revolutionize biosensing applications, specifically in medical diagnostics. Optical sensors can be designed to improve clinically-relevant diagnostic assays and be functionalized to capture and detect target biomarkers of interest. There are various approaches to designing these sensors - improving the devices' performance, increasing the interaction of light with the analyte, and matching the characteristics of the biomolecules by using architectures that complement the biosensing application. Using e-beam lithography and standard foundry processes, we have investigated Transverse Magnetic (TM) and Transverse Electric (TE) disk and ring resonators. TM devices hold the potential for higher sensitivity and large-particle sensing capabilities due to the increased penetration distance of light into the analyte. In addition, devices such as slot wavegguide Bragg grating sensors have shown high sensitivities and high quality factors and may present advantages for specific biosensing applications. These devices have been investigated for wavelengths around λ=1550 nm (conventional wavelength window in fiber-optic communication) and λ=1220 nm, where the water absorption is greatly decreased, offering improved limits of detection. Using reversibly bonded PDMS microfluidic flow cells, the performance and bio-detection capabilities of these devices were characterized. Comparing binding performance across these devices will help validate architectures suitable for biological applications. The most promising sensors for each application will then be identified for further study and development. This paper will discuss the sensors' comparative advantages for different applications in biosensing and provide an outlook for future work in this field.
We present an extensive study of an Er doped Silicon Rich Silicon Oxide (SRSO) based material used for the realization of
optical waveguide amplifiers in which Si-nanoclusters (Si-ncls) are formed by thermal annealing. In particular we focus our
attention on the confined carrier absorption (CCA) mechanism within the Si-ncls and on the fraction of Er ions coupled to
them. Experimental data are used for accurate modeling of Si-ncls sensitized EDWAs (Erbium Doped Waveguide
Amplifiers) longitudinally pumped by visible broad area lasers.
Although the material requires further optimization to be effectively deployed, accurate numerical simulations of Si-ncls
sensitized EDWAs, based on this material and longitudinally pumped by visible broad area lasers at 660 nm, point out
significant benefits provided by the nanoclusters sensitization. Our model, based on the Finite Element Method, performs the
modal analysis of the guiding structure, and then allows to study the propagation of pump and signal electric fields along the
waveguide amplifier; the rate equations for the coupled Er/Si-ncls system account for their coupling ratio.
Numerical results, based on measured material parameters, point out that resonant pumping at 660 nm provides significant
benefits in terms of gain enhancement, with respect to standard EDWAs, even at low Er/Si-ncls coupling ratio. This feature
suggests that a careful design can lead to the realization of compact integrated amplifiers and lasers, compatible with CMOS