One of the key challenges in the field of silicon photonics remains the development of compact integrated light sources. In one approach, rare-earth-doped glass microtoroid and microdisk lasers have been integrated on silicon and exhibit ultra-low thresholds. However, such resonator structures are isolated on the chip surface and require an external fiber to couple light to and from the cavity. Here, we review our recent work on monolithically integrated rare-earth-doped aluminum oxide microcavity lasers on silicon. The microlasers are enabled by a novel high-Q cavity design, which includes a co-integrated silicon nitride bus waveguide and a silicon dioxide trench filled with rare-earth-doped aluminum oxide. In passive (undoped) microresonators we measure internal quality factors as high as 3.8 × 105 at 0.98 µm and 5.7 × 105 at 1.5 µm. In ytterbium, erbium, and thulium-doped microcavities with diameters ranging from 80 to 200 µm we show lasing at 1.0, 1.5 and 1.9 µm, respectively. We observe sub-milliwatt lasing thresholds, approximately 10 times lower than previously demonstrated in monolithic rare-earth-doped lasers on silicon. The entire fabrication process, which includes post-processing deposition of the gain medium, is silicon-compatible and allows for integration with other silicon-based photonic devices. Applications of such rare earth microlasers in communications and sensing and recent design enhancements will be discussed.
We demonstrate a hybrid integrated photonic-plasmonic platform in which photonic guided modes are used to efficiently
excite localized surface plasmon resonance (LSPR) modes of plasmonic nanoresonators. Efficient coupling of light to
the LSPR modes of plasmonic nanoresonators is demonstrated by tight integration of plasmonic nanoresonators on
silicon nitride (SiN) microresonators. It is shown that by integrating gold nanoparticles with SiN microresonators, we
can achieve high coupling efficiencies (>35%), resulting in large field enhancements. We will discuss the design,
fabrication, and characterization of the hybrid platform which consists of gold nanoparticles integrated with SiN
microring resonators.
We report the demonstration of a cascaded configuration to realize wideband high-resolution spectrometers in silicon-nitride
for the visible range. The cascaded configuration consists of an arrayed waveguide grating followed by a set of
resonators and offers a flexibility to achieve the requirements of different sensing applications. We discuss some of the
implementation issues of these structures. A preliminary demonstration shows the capability of such spectrometer
devices to achieve ~0.1 nm wavelength resolution over 10 nm bandwidth in a compact device in a mm-scale device.
The potentials of a nanophotonic platform, including compactness, low power consumption, integrability with other functionalities, and high sensitivity make them a suitable candidate for sensing applications. Strong light-matter interaction in such a platform enables a variety of sensing mechanisms, including refractive index change, fluorescence emission, and Raman scattering. Recent advances in nanophotonic devices include the demonstration of silicon and silicon-nitride microdisk resonators with high intrinsic Q values (0.5-2×106) for strong field enhancement and the realization of compact photonic crystal spectrometers (high spectral resolution at 100-µm length scales) for on-chip spectral analysis. These two basic building blocks, when combined with integrated fluidic channels for sample delivery, provide an efficient platform to implement different sensing mechanisms and architectures.
The potentials of integrated optical systems for implementing compact and low power consumption yet highly sensitive
sensing systems have made them a viable candidate for integrated chemical and biological sensing applications. In these
integrated optical sensing systems, spectrometers have a significant role as a building block that enables on-chip
spectral analysis. Monitoring the spectral features of the signal using an on-chip spectrometer brings about a variety of
new sensing mechanisms and architectures in an integrated platform. Monitoring absorption spectra, measuring Raman
emission features, and tracking changes in spectral signatures as a result of environmental changes are some of the
schemes made possible by such spectral analysis. In this work, we implement superprism-based photonic crystal devices
in planar platforms as on-chip spectrometers. We use planar silicon platform in a silicon-on-insulator (SOI) wafers for
the infrared wavelength range. A silicon-nitride (SiN) planar platform is used for the near infrared and visible
wavelength ranges. In both SOI and SiN implementations, superprism-based spectrometers are experimentally
demonstrated and compared with grating spectrometers made in the same platform. The potentials of the demonstrated
spectrometers to meet the requirements of current and future applications in integrated optical sensing are briefly
discussed.
The opportunity to manipulate optical properties of materials through fabrication is the unique capability offered by
photonic crystals. Among different directions to exploit the possibilities in this field, there have been recent research
activities to engineer the dispersive properties of photonic crystals to change the propagation properties of waves
passing through these periodic structures. To provide an efficient way to implement such devices, an approximate
modeling technique will be used to simplify the analysis and design process for dispersive photonic crystal devices.
Furthermore, the issue of efficient coupling to dispersive photonic crystal modes which is crucial for practical
implementation of these devices will be addressed. Here, in particular, we will focus on employing the dispersive
properties of photonic crystals to realize compact optical spectrometers and wavelength demultiplexers. We will show
that by combining multiple dispersive properties (i.e., negative diffraction and the superprism effect) it is possible to
enhance the performance of devices targeted for such applications. The potentials of these photonic crystal devices to
meet the requirements of current and future applications in optical information processing and integrated optical sensing
will be discussed.
Photonic crystal waveguides (PCW) on silicon-on-insulator (SOI) are considered as a promising guiding platform with
flexible guiding properties for dense photonics integration. Although SOI is a versatile material for photonics
integration, PCWs fabricated on SOI substrates suffer from small guiding bandwidth due to the coupling to leaky TM-like
modes. The purpose of this work is to present a systematic approach to increase the low-loss guiding bandwidth of
PCWs on SOI. This has been achieved by reducing the interaction of low-group-velocity modes with the surrounding
photonic crystal. By this method the low-loss bandwidth of a W1 PCW is increased from 2.5 nm to 12 nm which is the
highest reported for this type of waveguide. We also present a detailed analysis of transmission properties of W1 PCWs
and elaborate on the coupling to TM-like guided modes present in the low-loss transmission bandwidth of this device.
Compact on-chip wavelength demultiplexers and spectrometers are essential components for a variety of applications
including integrated optical information processing devices, optical communications, and integrated optical sensing.
Implementation of such devices requires strong dispersion in the optical materials, which can be realized using unique
dispersive properties of photonic crystals (PCs). Possibility of integration, compactness, and compatibility with different
host materials are the main advantages of PC based demultiplexers and spectrometers compared to other techniques.
Here, we show an implementation of superprism-based photonic crystal devices (using a diffraction compensation
scheme) that improves the performance of these devices compared to the conventional implementation. Structures
obtained through optimization have been fabricated in SOI wafers using e-beam writing and ICP etching, and spatial
separation of channels (with good isolation) in these superprism devices is experimentally demonstrated. The
performance of these superprism devices as general-purpose spectrometers and for locating spectral features in a
sensing platform will be also demonstrated and discussed. Further steps for improvement of these devices are
considered and the related implementation issues are investigated.
We show that simultaneous perturbation of periodicity and radius of air holes next to the guiding region in a photonic
crystal waveguide results in low loss and large bandwidth waveguides that are also single mode. We also show the
results of a single shot spectral phase measurement that can be used for real time dispersion measurement of photonic
crystal waveguides.
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