Silicon photonics is gaining increasing adoption for mid- to long-reach communication links in datacenters at 100Gbps and beyond. Two significant challenges remain integrated on-chip WDMs, and fiber and laser packaging.
The adoption of wavelength division multiplexing (WDM) allows for multiple data signals to be carried on a single fiber, reducing the cost of fiber provisioning compared to parallel implementations and greatly increasing achievable data rates. Designing WDM structures can be challenging on a silicon platform, however, as silicon waveguides are highly sensitive to minute fabrication variations and temperature changes. To account for and compensate for these changes, it is necessary to have a robust testing methodology to characterize the WDM system, as well as an efficient and complete tuning mechanism to dial in the desired performance without sacrificing too much in power consumption, chip area for off-chip electrical connections, and insertion loss. We will present a monolithic silicon WDM design, the implementation of low power tuning elements, and the test and biasing algorithms to align all filters on the desired CWDM grid.
Another perennial challenge for silicon photonics has been coupling light on and off the chip, due to the significant mode size mismatch and exacting alignment requirements between silicon waveguides and optical fibers or III-V chips. We will present on packaging developments implementing fully passive alignment using existing CMOS production tools, improving scalability and cost efficiency and enabling the packaging techniques for silicon photonics chips to keep up with the massive volumes generated by silicon waferscale fabrication.
Silicon photonics is rapidly becoming the key enabler for meeting the future data speed and volume required by the Internet of Things. A stable manufacturing process is needed to deliver cost and yield expectations to the technology marketplace. We present the key challenges and technical results from both 200mm and 300mm facilities for a silicon photonics fabrication process which includes monolithic integration with CMOS. This includes waveguide patterning, optical proximity correction for photonic devices, silicon thickness uniformity and thick material patterning for passive fiber to waveguide alignment. The device and process metrics show that the transfer of the silicon photonics process from 200mm to 300mm will provide a stable high volume manufacturing platform for silicon photonics designs.
μWe report the demonstration of multi-spectral quantum dots-in-a-well infrared photo-detectors through the coupling of
incident light to resonant modes of surface plasmons. The integration of a surface plasmon assisted cavity with the detector
results in shifting the peak wavelength of absorption of the detector to that of the resonant wavelength of the cavity. The
cavity consists of a square lattice structure with square holes in it. A wavelength tuning of 8.5 to 9 μm was observed,
by changing the pitch of the fabricated pattern forming the cavity. Polarization sensitive detectors can be fabricated by
breaking the symmetry of the lattice. This is achieved by stretching the lattice constants along the x and y directions. A
DWELL detector with resonant frequency at 6.8 μm where the response of the 0 ° polarization is twice as strong as the 90°
polarization is reported. This technique, in principle, is detector agnostic and shows promise in fabrication of multi-spectral
focal plane arrays (FPA).
We report Quantum Dot Infrared Detectors (QDIP) where light coupling to the self assembled quantum dots
is achieved through plasmons occurring at the metal-semiconductor interface. The detector structure consists
of an asymmetric InAs/InGaAs/GaAs dots-in-a-well (DWELL) structure and a thick layer of GaAs sandwiched
between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The aperture of
the detector is covered with a thin metallic layer which along with the dielectric layer confines light in the vertical
direction. Sub-wavelength two-dimensional periodic patterns etched in the metallic layer covering the aperture
of the detector and the active region creates a micro-cavity that concentrate light in the active region leading
to intersubband transitions between states in the dot and the ones in the well. The sidewalls of the detector
were also covered with metal to ensure that there is no leakage of light into the active region other than through
the metal covered aperture. An enhanced spectral response when compared to the normal DWELL detector
is obtained despite the absence of any aperture in the detector. The spectral response measurements show
that the Long Wave InfraRed (LWIR) region is enhanced when compared to the Mid Wave InfraRed (MWIR)
region. This may be due to coupling of light into the active region by plasmons that are excited at the metal-semiconductor
interface. The patterned metal-dielectric layers act as an optical resonator thereby enhancing the
coupling efficiency of light into the active region at the specified frequency. The concept of plasmon-assisted
coupling is in principle technology agnostic and can be easily integrated into present day infrared sensors.